Spiral of silence

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The spiral of silence theory is a political science and mass communication theory proposed by the German political scientist Elisabeth Noelle-Neumann. It states that an individuals perception of the distribution of public opinion influences that individuals willingness to express their own political opinions. The main idea is that people have an influence on each other's willingness to express opinion through social interaction. According to the spiral of silence theory, individuals will be more confident and outward with their opinion when they notice that their own personal opinion is shared throughout a group, but if the individual notices that their opinion is unpopular with the group they will be more inclined to be more reserved and remain silent. The individual "not isolating himself is more important than his own judgement". This is a self-expressive act that can change the "global environment of opinion", shifting the perceptions of others and the willingness of individuals to express their own opinions.

According to Glynn (1995), "the major components of the spiral of silence include (1) an issue of public interest; (2) divisiveness on the issues; (3) a quasi-statistical sense that helps an individual perceive the climate of opinion as well as estimate the majority and minority opinion; (4) "fear of isolation" from social interaction; (5) an individual's belief that a minority (or "different") opinion isolates oneself from others; and (6) a "hardcore" group of people whose opinions are unaffected by others' opinions."

Background

In 1974, Elisabeth Noelle-Neumann, a German political scientist, created the famous model called “Spiral of Silence”. She believed that an "individuals willingness to express his or her opinion was a function of how he or she perceived public opinion." In 1947, Neumann and her husband founded “Public Opinion Organization” in Germany. She was also a President of the “World Association for Public Opinion Research” from 1978 to 1980.

Noelle-Neumann evolved the spiral of silence theory from research of the 1965 West German elections. The research, according to Noelle-Neumann, "measured a lot more than we understood." The two major parties were locked in a dead heat from December until September, with a series of questions of public perception of the election winner was showing steady, independent movement. During the final days of the election, 3 to 4% of the voters shifted in the direction of the public's perception of the winner. A similar theme happened in the 1972 election, which began the development of the spiral of silence as a theory of public opinion.

According to Shelly Neill, "Introduced in 1974, the Spiral of Silence Theory [...] explores hypotheses to determine why some groups remain silent while others are more vocal in forums of public disclosure." The spiral of silence theory suggests that "people who have believed that they hold a minority viewpoint on a public issue will remain in the background where their communication will be restrained; those who believe that they hold a majority viewpoint will be more encouraged to speak." The spiral of silence theory arose from a combination of high public uncertainty about a topic with an increase in the flow of communication.

The theory explains the formation of social norms at both the micro and macro level. "As a micro-theory, the spiral of silence examines opinion expression, controlling for people's predispositions – such as fear of isolation, and also demographic variables that have been shown to influence people's willingness to publicly express opinions on issues, such as agricultural biotechnology." The spiral of silence occurs on a macro level if more and more members of the perceived minority fall silent. This is when public perceptions of the opinion climate begin to shift. "In other words, a person's individual reluctance to express his or her opinion, simply based on perceptions of what everyone else thinks, has important implications at the social level." As one opinion gains interest, the amount of exposure it receives increases, leading the public to believe it to be the majority. The perceived minority then faces the threat and fear of isolation from society unless they conform. As the opinion gains momentum, the perceived minority falls deeper into their silence. This continues until the perceived minority no longer speaks out against it, either by presenting an image of agreement or actually conforming, and the opinion of the perceived majority ultimately becomes a social norm.

Since then, a large amount of research has been done by Glynn (1983, 1989), Glynn and McLeod (1985), Katz (1983), LaSora (1991), Price and Allen (1990), Salmon and Kline (1985), Taylor (1982), and Kennamer (1990).

Spiral model

The spiral model is used to visually describe the theory. An individual is more likely to go down the spiral if his or her opinion does not conform with the perceived majority opinion. The following steps summarize how the process works:

1. The model begins with individuals' inherent desire to blend with society. The fear of social isolation is necessary for the spiral to occur.
2. Individuals who notice that their personal opinion is spreading will voice this opinion confidently in public. On the other hand, individuals who notice that their opinions are losing ground will be inclined to adopt a more reserved attitude when expressing their opinions in public.
3. Representatives of the spreading opinion talk quite a lot while the representatives of the second opinion remain silent. An opinion that is being reinforced in this way appears stronger than it really is, while an opinion suppressed will seem to be weaker than it really is.
4. The result is a spiral process which prompts other individuals to perceive the changes in opinion and follow suit until one opinion has become established as the prevailing attitude while the other opinion will be pushed back and rejected by most. The end of the spiral refers to the number of people who are not publicly expressing their opinions, due to the fear of isolation.

This is a process of formation, change, and reinforcement of public opinion. The tendency of the one to speak up and the other to be silent starts off a spiraling process which increasingly establishes one opinion as the dominant one. Over time, these changing perceptions establish one opinion as predominant one and they change from the liquid state to a solid norm.

Further, Noelle-Neumann describes the spiral of silence as a dynamic process, in which predictions about public opinion become fact as mass media's coverage of the majority opinion becomes the status quo, and the minority becomes less likely to speak out.

Momentum Effect

The basic ideas for the spiral of silence is not unique. In 1987, Kerr, MacCoun, Hansen and Hymes brought to light the idea of the "momentum effect". The momentum effect states that if some members of a group move toward a particular opinion, others will follow. Others have described similar "gain-loss effect" (Aronson & Linder, 1965), and "bandwagon effect" (Myers & Lamm, 1976).

Epistemology

Public

Scholars have long argued over the concept of public within "public opinion". The use of "public" and "the public" betrays multiple competing meanings. There are three meanings of public. One meaning is the legal sense of public that focuses on openness. For example, a public place or path. A second meaning for the term emphasizes public rights. Lastly, within the phrase public opinion, public is said to have a related but different definition. Public, in this sense, could be characterized as social psychology. Scholars have marveled in amazement at the power public opinion has in making regulations, norms, and moral rules triumph over the individual self without ever troubling legislators, governments, or courts for assistance.

Opinion

"Common Opinion" is what the Scottish social philosopher David Hume called it in his 1739 published work A Treatise of Human Nature. Agreement and a sense of the common are what lay behind the English and French "opinion." In researching the term opinion, Meinung in German, researchers were led back to Plato's Republic. In Plato's Republic, a quote from Socrates conclude that opinion takes the middle position. Immanuel Kant considered the opinion to be an "insufficient judgment, subjectively as well as objectively." How valuable opinion may be was left out; however, the fact that it is suggested to be unified agreement of a population or segment of the population, was still considered.

Public opinion

The term public opinion first emerged in France during the eighteenth century. The definition of public opinion has been debated over time. There has not been much progress in locking in one classification of the phrase public opinion. Hermann Oncken, a German historian, stated

Whoever desires to grasp and define the concept of public opinion will recognize quickly that he is dealing with a Proteus, a being that appears simultaneously in a thousand guises, both visible and as a phantom, impotent and surprisingly efficacious, which presents itself in innumerable transformations and is forever slipping through our fingers just as we believe we have a firm grip on it... That which floats and flows cannot be understood by being locked up in a formula... After all, when asked, everyone knows exactly what public opinion means.

It was said to be a "fiction that belonged in a museum of the history of ideas; it could only be of historical interest."

In contradiction to that quote, the term public opinion seemed to not cease. During the early 1970s, Elisabeth Noelle-Neumann was creating the theory of the spiral of silence. She was attempting to explain why Germans who disagreed with Hitler and the Nazi's (many did) remained silent until after his regime ended. This "two-faced" behavior has come to be known as the spiral of silence theory. Noelle-Neumann began to question if she was indeed grabbing a handle on what public opinion actually was. "The spiral of silence might be one of the forms in which public opinion appeared; it might be a process through which a new, youthful public opinion develops or whereby the transformed meaning of an old opinion spreads."

The American sociologist Edward Ross described public opinion in 1898 using the word "cheap". "The equation of 'public opinion' with 'ruling opinion' runs like a common thread through its many definitions. This speaks to the fact that something clinging to public opinion sets up conditions that move individuals to act, even against their own will."

Many possible meanings and definitions of the term have been explored. Scholars have considered the content of public opinion, assumed to consist of public affairs issues. Scholars point out that the emergence of the public opinion depends on an open public discourse rather than "on the discipline imposed by an apparent majority dominant enough to intimidate but whose views may or may not support actions that are in the common interest."

They have also considered whose opinion establishes public opinion, assumed to be persons of a community who are ready to express themselves responsibly about questions of public relevance. Scholars have also looked into the forms of public opinion, said to be those that are openly expressed and accessible; opinions that are made public, especially in the mass media. Controversy surrounding this term spiraled around both words combining to form the phrase.

Neumann (1955) suggests two concepts on public opinion:

Public Opinion as Rationality: The public opinion or "dominant view" comes after conscious rational public discussion. Childs (1965) and Wilson (1933) believe that "the rational model is based on the notion of an enlightened, rational public that is willing to and capable of participating in political processes." In all, it is political and necessary for generating social change.

Public Opinion as Social Control: This is at the root of the Spiral of Silence Theory. It means that "opinions that can be expressed without risking sanctions or social isolation, or opinions that have to be expressed in order to avoid isolation (Noelle-Neumann 1983). Social systems require cohesion. To achieve this, individuals are threatened with social isolation.

Media and public opinion

Mass media's effects on both public opinion and the perception of the public opinion are central to the Spiral of Silence Theory. One of the earliest works that called attention to the relationship between media and the formation of public opinion was Walter Lippmann's book "Public Opinion," published in 1922. Ideas of Lippmann regarding the effects of media influenced the emergence of the Spiral of Silence Theory. As she is building the spiral theory, Noelle-Neumann states "the reader can only complete and explain the world by making use of a consciousness which in large measure has been created by the mass media."

Agenda-setting theory is another work that Noelle-Neumann builds on as she is characterizing media's effect on the public opinion. Agenda-setting theory describes the relationship between media and public opinion by asserting that the public importance of an issue depends on its salience in the media. Along with setting the agenda, the media further determine the salient issues through a constant battle with other events attempting to gain place in the agenda. The media battle with these news alternatives by creating "pseudo-crises" and "pseudo-novelties."

Media's characteristics as a communication tool further affect people's perception of their own ideas in regard to the public opinion. According to Noelle-Neumann, the media are a "one-sided, indirect, public form of communication, contrasting threefold with the most natural form of human communication, the conversation." When an issue hits the media and proves salient, a dominant point of view usually emerges. These characteristics of the media in particular further overwhelm one's individual ideas.

While some media communication theories assume a passive audience, such as the Hypodermic Needle model, the spiral model assumes an active audience "who consumes media products in the context of their personal and social goals." Knowledge "gained from the mass media may offer ammunition for people to express their opinions and offer a rationale for their own stance." Ho et al. point out that "among individuals who paid high amount of media attention, those who have a low fear of isolation were significantly more likely to offer a rationale for their own opinion than were those who have a high fear of isolation."

Noelle-Neuman regards media central to the formulation of the Spiral of Silence Theory, whereas some scholars argue whether the dominant idea in one's social environment overwhelms the dominant idea that media propose as the perceived social norm. Some empirical research align with this perspective; suggesting that the "micro-climate" of an individual overwhelms the effects of the media. Other articles further suggest that talking with others is the primary way of understanding the opinion climate.

Social Media has contributed to the Spiral of Silence Theory. Researchers, Chaudhry & Gruzd (2019) found that social media actually weakens this theory. This theory suggests that the minority are uncomfortable expressing their opinions because of the fear of isolation, but, "the vocal minority are comfortable expressing unpopular views, questioning the explanatory power of this popular theory in the online context."

Perception

The Spiral of Silence Theory rests on perception as individuals constantly scan their environment to assess the climate to possibly find the dominant point of view. Perception matters because these opinions influence an individual's behavior and attitudes. How can individuals do this? Sherif (1967) believes individuals use frames of reference based on past experience -- "social environment as a frame of reference for interpreting new information has important implications for public opinion research." According to Gestalt psychology, when individuals are presented with information with "an appropriate frame of reference by which to interpret it" they are uncomfortable in the social environment (e.g. behavioral influence).

Assumptions

Fear of isolation

The spiral of silence can lead to a social group or society isolating or excluding members due to the members' opinions. This stipulates that individuals have a fear of isolation. This fear of isolation consequently leads to remaining silent instead of voicing opinions. Media are an important factor that influence both the dominant idea and people's perception of what the dominant idea is. The assessment of one's social environment may not always correlate with reality.

The fear of isolation is the "engine that drives the spiral of silence". Essentially, people fear becoming social isolates and thus take measures to avoid such a consequence, as demonstrated by psychologist Solomon Asch in the Asch conformity experiments. People feel more comfortable agreeing with the dominant opinions instead of expressing their own ideas.

An underlying idea of the spiral of silence theory is that public opinion acts as a form of social control. According to Noelle-Neumann's definition this key concept describes "opinions on controversial issues that one can express in public without isolating oneself". This assumption supposed that public opinion is governed by norms and conventions, the violation of which will lead to sanctions against those individuals. Going off of this assumption that going against public opinion will lead to social sanctions, Noelle-Neumann assumes that human beings have an inherent fear of isolation and will adapt their behavior so that they will not be isolated from others. This “fear of isolation” is so strong that people will not express opinions if they assume that these opinions differ from public opinion.

Based on this assumption it follows that people will constantly monitor their social environment in order to assess whether their opinion diverges from public opinion and will decide whether or not to voice their opinion based on their assessment of the public opinion on an issue. Noelle-Neumann attributed this ability of assessing opinion climate on an issue to the so-called "quasi-statistical organ", which refers to how individuals unconsciously assess the distribution of viewpoints and the chances that certain viewpoints will succeed over others. According to Noelle-Neumann everyone is affected by this fear of isolation and the ensuing self-censoring except for about 25% of the general population which she refers to as “hardcores” who are assumed to be immune to this social pressure.

This fear of social isolation is a central concept in Noelle-Neumann's theory but throughout different studies on the theory it has been conceptualized in many different ways. Some researchers have considered fear of social isolation to be transitory and triggered by the exposure to a situation in which an individual is expected to express an opinion. In this conceptualization an individual's perception of the opinion climate in a specific situation would trigger the fear of isolation in that moment.

Other researchers have argued that instead of a situation specific reaction, fear of social isolation can be viewed as individual characteristic that varies between people and leads individuals to continuously monitor their environment for cues about the opinion climate. While there are individuals who generally do not suffer from a fear of isolation (what Noelle-Neumann referred to as Hardcores, others are constantly aware of their social environment and faced with a constant fear of isolation. Individuals who bear this characteristic of fear of social isolation and at the same time perceive their opinion to be incongruent with the majority opinion climate are less likely to be willing to voice their opinion. Similar to the previously described conceptualization of fear of social isolation, in this line of spiral of silence research fear of social isolation is a key concept in formation of public opinion, however research has often assumed this conceptualization as a fact without empirical proof or been inconsistent in the empirical measurement of this phenomenon.

Recent research has been able to capture the concept of fear of social isolation in a more reliable and consistent way. One example is research conducted by Mathes (2012) in which the researchers used an individual differences approach based on individual's character traits and measured individual's fear of social isolation using psychometric properties. Mathes (2012), as well as other researchers, considers fear of social isolation to be a subsequent reaction to encountering a perceived hostile opinion climate which in turn leads the individual to not voice their own opinions and therefore sets in motion the spiral of silence.

Assessing the climate

This assumption proposes that in order to avoid becoming isolated and in order not to lose popularity and esteem, people constantly observe their environment very closely. They try to find out which opinions and modes of behaviour are prevalent, and which opinions and modes of behaviour are becoming more popular. They behave and express themselves accordingly in public. Then, they try to determine whether they are in the majority: whether the public opinion tends to agree with them. If they feel they are in the minority, they tend to remain silent.

Quasi-statistical sense

Described as a "sixth-sense," individuals use what is described as "an innate ability" or quasi-statistical sense to gauge public opinion. People assume they can sense and figure out what others are thinking.

The Mass media play a large part in determining what the dominant opinion is, since our direct observation is limited to a small percentage of the population. The mass media have an enormous impact on how public opinion is portrayed, and can dramatically impact an individual's perception about where public opinion lies, whether or not that portrayal is factual.

Pluralistic ignorance

Pluralistic ignorance may occur in some cases, leading to the minority opinion to be accepted as a norm. Group members may be privately rejecting a norm, but may falsely assume that other group members accept it. This phenomenon may cause a group to hold on to a norm.

Evaluation of public opinion matters

Our evaluation of a public opinion has an effect on our decision to speak up. Where opinions are relatively definite and static – customs, for example – one has to express or act according to this opinion in public or run the risk of becoming isolated. In contrast, where opinions are in flux, or disputed, the individual will try to find out which opinion he can express without becoming isolated. Individuals tend to publicly express their opinions and attitudes when they perceive their view to be dominant or on the rise. Conversely, when individuals perceive that their opinion is less popular or losing popularity, they are less likely to voice it in public. What one individual decides to do affects all of society around them.

Vocal minority and hardcore

The theory explains a vocal minority (the complement of the silent majority) by stating that people who are highly educated, or who have greater affluence, and the few other cavalier individuals who do not fear isolation, are likely to speak out regardless of public opinion. It further states that this minority is a necessary factor of change while the compliant majority is a necessary factor of stability, with both being a product of evolution. There is a vocal minority, which remains at the top of the spiral in defiance of threats of isolation.

This theory calls these vocal minorities the hardcore nonconformist or the avant-garde. Hardcore nonconformists are "people who have already been rejected for their beliefs and have nothing to lose by speaking out." The hardcore has the ability to reconfigure majority opinion. While the avant-garde are "the intellectuals, artists, and reformers in the isolated minority who speak out because they are convinced they are ahead of the times."

Application of the theory

The spiral of silence has brought insight regarding diverse topics, ranging from speaking about popular culture phenomena, to smoking. Considering that the spiral of silence is more likely to occur in controversial issues and issues with a moral component, many scholars have applied the theory to controversial topics, such as abortion, affirmative action, and capital punishment. Mandatory Covid vaccines and masking.

Cross cultural studies

Existing literature prior to the spiral of silence theory suggest a relationship between social conformity and culture, motivating communication scholars to conduct cross-cultural analysis of the theory. Scholars in the field of psychology in particular previously addressed the cultural variance involved in the conformity to the majority opinion. More recent studies confirm the link between conformity and culture: a meta-analysis regarding Asch conformity experiments, for example, suggest that collectivist cultures are more likely to exhibit conformity than the individualistic cultures.

The United States and Taiwan

A Cross Cultural Test of the Spiral of Silence by Huiping Huang analyzes the results of a telephone survey done in Taiwan and the United States. The hypotheses tested were the beliefs that the United States is an "individualistic" society, while Taiwan is a "collectivist" society. This suggested that the spiral of silence is less likely to be activated in the United States, because individuals are more likely to put emphasis on their personal goals. They put the "I" identity over the "we" identity, and strive for personal success. Therefore, it was hypothesized that they would be more likely to speak out, regardless of if they are in the minority. On the other hand, it was predicted that individuals in Taiwan put more emphasis on the collective goal, so they would conform to the majority influence in hopes of avoiding tension and conflict. The study also tested the effect of motives, including self-efficacy and self-assurance.

Telephone surveys were conducted; the citizens of the United States were questioned in regards to American involvement in Somalia, and the citizens of Taiwan about the possibility of a direct presidential election. Both issues focused on politics and human rights, and were therefore comparable. Respondents were asked to choose "favor," "neutral" or "oppose" in regards to the categories of themselves, family and friends, the media, society, and society in the future about the given issue. Measurements were also taken regarding the individualism and collectivism constructs, and the "motives of not expressing opinion" based on a 1–10 and 1–5 scale respectively, in approval of given statements.

Results showed support for the original hypothesis. Overall, Americans were more likely to speak out than Taiwanese. Being incongruous with the majority lessened the motivation of the Taiwanese to speak out (and they had a higher collectivist score), but had little effect on the Americans. In Taiwan, future support and belief of society played a large role in likeliness to voice an opinion, and support that the activation of the spiral of silence is in effect. In the United States, it was hypothesized that because they were more individualistic, they would be more likely to speak out if in the minority, or incongruous group. However, this was not true, but Huang suggests that perhaps the issue chosen was not directly prevalent, and therefore, they found it "unnecessary to voice their objections to the majority opinion." Lack of self-efficacy led to lack of speaking out in both countries.

Basque nationalism

Basque Nationalism and the Spiral of Silence is an article by Spencer and Croucher that analyzes the public perception of ETA (Euskadi Ta Askatasuna, a militant separatist group) in Spain and France. This study was conducted in a similar way as above, with Basque individuals from Spain and France being questioned about their support of ETA. They were asked questions such as "How likely would you be to enter into a conversation with a stranger on a train about ETA?" Taken into consideration were the cultural differences of the two different regions in which ETA existed.

The results supported the theory of the spiral of silence. While there was a highly unfavorable opinion of the group, there was a lack of an outcry to stop it. Individuals claimed that they were more likely to voice their opinions to non-Basques, suggesting that they have a "fear of isolation" in regards to fellow Basques. Furthermore, the Spanish individuals questioned were more likely to be silent because of their greater proximity to the violent acts.

Perceptions in the classroom

One study, by Henson and Denker "investigates perceptions of silencing behaviors, political affiliation, and political differences as correlates to perceptions of the university classroom climates and communication behaviors." They looked at whether students' view of the classroom changes whether they perceive the instructor and other classmates with a different political affiliation, with the instructor and other classmates communicating using silencing behaviors. The article stated that little has been investigated into student-teacher interactions in the classroom, and how the students are influenced. The goal of the article was to "determine how political ideas are expressed in the university classrooms, and thus, assess the influence of classroom communication on the perceptions of political tolerance."

The article claimed that university classrooms are an adequate place to scrutinize the spiral of silence theory because it is a place that has interpersonal, cultural, media, and political communication. Henson and Denker said, "Because classroom interactions and societal discourse are mutually influential, instructors and students bring their own biases and cultural perspectives into the classroom."

The study researched whether there was a correlation between students' perception that they were being politically silenced and their perceived differences in student-instructor political affiliation. The study also questioned whether there was any connection between the perceived climate and the similarity of the student and instructor on their political affiliations. The researchers used participants from a Midwestern university's communication courses. The students answered a survey over their perceptions of political silencing, classroom climate, and the climate created by the instructor. The results of this research found that there is a positive relationship of the perceived similarities in a political party and ideological differences of the student and instructor to perceived greater political silencing.

In computer-mediated communication

While the studies regarding the spiral of silence theory focused on face-to-face interaction before 2000, the theory was later applied to a computer-mediated communication environment. The first study in this context analyzed communication behaviors in online chat rooms regarding the issue of abortion, and revealed that minority opinion holders were more likely to speak out, whereas their comments remained neutral. Another study focused on the Korean bulletin board postings regarding the national election, and found a relationship between online postings and the presentation of candidates in the mainstream media. The third study focuses on the online review system, suggesting that the fear of isolation tend to reduce the willingness of members to voice neutral and negative reviews. The Spiral of Silence Theory is extended "into the context of non-anonymous multichannel communication platforms" and "the need to consider the role of communicative affordances in online opinion expression" is also addressed.

In social media contexts

Current literature suggests that the spiral model can be applied to the social media context. Gearhart and Zhang conduct a study to examine whether or not the use of social media will increase people's motivation to express their opinions about political issues. The results suggest that social media users "who have received a strong negative reaction to their politically related posts are likely to censor themselves, exemplifying the spiral of silence effect". Another research confirms the positive relationship between speaking out and issue importance on the social media context as well: individuals who view gay bullying as a significant social issue are more likely to comment on Facebook. As social media becomes more and more important in our daily lives, Deceptive social bots have been successfully applied for manipulating online conversations and opinions. Current research shows that "social bots" are being used on a large scale to control the opinion climate to influence public opinion on social media. Social bots are social media accounts managed by computer algorithms. They can automatically generate content and interact with human users, often impersonating or imitating humans. Research shows that a small number of social bots can easily direct public opinion on social media and trigger a spiral of silence model. For example, scholars find out that social bots can affect political discussion around the 2016 U.S. presidential election and the 2017 French presidential election.

Social capital

The spiral of silence theory can be also applied to social capital context. Recent studies see social capital as "a variable that enables citizens to develop norms of trust and reciprocity, which are necessary for successful engagement in collective activities". One study examines three individual-level indicators of social capital: civic engagement, trust and neighborliness, and the relationship between these indicators and people's willingness to express their opinions and their perception of support for one's opinions. The results suggest that civic engagement has a direct effect on people's willingness to express their opinions and neighborliness and trust had direct positive effects on people's perception of support for one's opinions. Also, the study shows that "only a direct (but not indirect) effect of civic engagement on opinion expression further highlights a potential difference between bonding and bridging social capital".

Internet

Isolating the factors that remove isolation

The concept of isolation has a variety of definitions, dependent upon the circumstances it is investigated in. In one instance the problem of isolation has been defined as social withdrawal, defined as low relative frequencies of peer interaction. Other researchers have defined isolation as low levels of peer acceptance or high levels of peer rejection. Research that considers isolation with regard to the Internet either focuses on how the Internet makes individuals more isolated from society by cutting off their contact from live human beings or how the Internet decreases social isolation of people by allowing them to expand their social networks and giving them more means to stay in touch with friends and family. Since the development of the Internet, and in particular the World Wide Web, a wide variety of groups have come into existence, including Web and Internet Relay Chat (IRC), newsgroups, multiuser dimensions (MUDs), and, more recently, commercial virtual communities. The theories and hypotheses about how Internet-based groups impact individuals are numerous and wide-ranging. Some researchers view these fast growing virtual chat cliques, online games, or computer-based marketplaces as a new opportunity, particularly for stigmatized people, to take a more active part in social life.

Traditionally, social isolation has been represented as a one-dimensional construct organized around the notion of a person's position outside the peer group and refers to isolation from the group as a result of being excluded from the group by peers. From children to adults, literature shows that people understand the concept of isolation and fear the repercussions of being isolated from groups of which they are a member. Fearing isolation, people did not feel free to speak up if they feel they hold dissenting views, which means people restrict themselves to having conversation with like-minded individuals, or have no conversation whatsoever. Witschge further explained, "Whether it is fear of harming others, or fear to get harmed oneself, there are factors that inhibit people from speaking freely, and which thus results in a non-ideal type of discussion, as it hinders diversity and equality of participants and viewpoints to arise fully."

The medium of the Internet has the power to free people from the fear of social isolation, and in doing so, shuts down the spiral of silence. One article proves out the social media can weaken the fear of isolation. The research shows that the vocal minority who hold racist viewpoints are willing to expressing unpopular views on Facebook. The Internet allows people to find a place where they can find groups of people with like mindsets and similar points of view. Van Alstyne and Brynjolfsson stated that "Internet users can seek out interactions with like-minded individuals who have similar values, and thus become less likely to trust important decisions to people whose values differ from their own." The features of the Internet could not only bring about more people to deliberate by freeing people of psychological barriers, but also bring new possibilities in that it "makes manageable large-scale, many-to-many discussion and deliberation." Unlike traditional media that limit participation, the Internet brings the characteristics of empowerment, enormous scales of available information, specific audiences can be targeted effectively and people can be brought together through the medium.

Online versus offline

The Internet is a place where many reference and social groups are available with similar views. It has become a place where it appears that people have less of a fear of isolation. One research article examined individuals' willingness to speak their opinion online and offline. Through survey results from 305 participants, a comparison and contrast of online and offline spiral of silence behaviors was determined. Liu and Fahmy stated that "it is easy to quit from an online discussion without the pressure of complying with the majority group." This is not to say that a spiral of silence does not occur in an online environment. People are still less likely to speak out, even in an online setting, when there is a dominant opinion that differs from their own. But people in the online environment will speak up if someone has a reference group that speaks up for them.

Online, the presence of one person who encourages a minority point of view can put an end to a spiral of silence. Studies of the spiral of silence in online behavior have not acknowledged that a person may be more likely to speak out against dominant views offline as well. The person might have characteristics that make them comfortable speaking out against dominant views offline, which make them just as comfortable speaking out in an online setting.

Although research suggests that people will disclose their opinions more often in an online setting, silencing of views can still occur. One study indicates that people on Facebook are less willing to discuss the Snowden and NSA stories than an offline situation such as a family dinner or public meeting. Another research article examined the influence of different opinion climates in online forums (opinion congruence with the majority of forum participants vs. website source) and found personal opinion congruence was more influential than the online site in which the forum is situated in. Nekmat and Gonzenbach said it might be worth researching whether the factors in these studies or other factors cause people to be more comfortable when it comes to speaking their mind while online.

Heterogeneity and anonymity

The nature of the Internet facilitates not only the participation of more people, but also a more heterogeneous group of people. Page stated, "The onward rush of electronic communications technology will presumably increase the diversity of available ideas and the speed and ease with which they fly about and compete with each other." The reason people engage in deliberations is because of their differences, and the Internet allows differences to be easily found. The Internet seems the perfect place to find different views of a very diverse group of people who are at the same time open to such difference and disagreement needed for deliberation. Noelle-Neumann's initial idea of cowering and muted citizens is difficult to reconcile with empirical studies documenting uninhibited discussion in computer-mediated contexts such as chat rooms and newsgroups.

The Internet provides an anonymous setting, and it can be argued that in an anonymous setting, fears of isolation and humiliation would be reduced. Wallace recognized that when people believe their actions cannot be attributed to them personally, they tend to become less inhibited by social conventions and restraints. This can be very positive, particularly when people are offered the opportunity to discuss difficult personal issues under conditions in which they feel safer.

The groups' ability to taunt an individual is lessened on the Internet, thus reducing the tendency to conform. Wallace goes on to summarize a number of empirical studies that do find that dissenters feel more liberated to express their views online than offline, which might result from the fact that the person in the minority would not have to endure taunts or ridicule from people that are making up the majority, or be made to feel uncomfortable for having a different opinion. Stromer-Galley considered that "an absence of non-verbal cues, which leads to a lowered sense of social presence, and a heightened sense of anonymity" frees people from the psychological barriers that keep them from engaging in a face-to-face deliberation.

The crux of the spiral of silence is that people believe consciously or subconsciously that the expression of unpopular opinions will lead to negative repercussions. These beliefs may not exist on the Internet for several reasons. First, embarrassment and humiliation depends on the physical presence of others. In computer-mediated communication, physical isolation often already exists and poses no further threat. Second, a great deal of normative influence is communicated through nonverbal cues, such as eye contact and gestures, but computer-mediated communication typically precludes many of these cues. Third, Kiesler, Siegel, and McQuire observe that nonverbal social context cues convey formality and status inequality in face-to-face communication. When these cues are removed, the importance of social status as a source of influence recedes. Group hierarchies that develop in face-to-face interaction emerge less clearly in a mediated environment. The form and consequences of conformity influence should undergo significant changes given the interposition of a medium that reduces the social presence of participants. Social presence is defined as the degree of salience of the other person in the interaction or the degree to which the medium conveys some of the person's presence.

Equality

An important issue in obtaining heterogeneity in conversation is equal access for all the participants and equal opportunities to influence in the discussion. When people believe they are ignorant about a topic, incapable to participate in a discussion or not equal to their peers, they tend to not even become involved in a deliberation. When people do decide to participate, their participation might be overruled by dominant others, or their contribution might be valued less or more, depending on their status. Dahlberg praises the Internet for its possibility to liberate people from the social hierarchies and power relations that exist offline: "The 'blindness' of cyberspace to bodily identity... [is supposed to allow] people to interact as if they were equals. Arguments are said to be assessed by the value of the claims themselves and not the social position of the poster".

Gastil sees this feature as one of the strongest points of the Internet: "if computer-mediated interaction can consistently reduce the independent influence of status, it will have a powerful advantage over face-to-face deliberation". While status cues are difficult to detect, perceptions about the status converge, and this lessens stereotyping and prejudice.

It may be that people do feel more equal in online forums than they feel offline. Racism, ageism, and other kinds of discrimination against out groups "seems to be diminishing because the cues to out-group status are not as obvious". Next to this, the Internet has rapidly and dramatically increased the capacities to develop, share and organize information, realizing more equality of access to information.

Methodological research approaches

The relationship between the perception of public opinion and willingness to speak-up is mainly measured through surveys In surveys, respondents are often asked whether they would reveal their opinions given a hypothetical situation, right after their opinions about the public opinion and their opinion is received. Whether asking hypothetical questions can reflect real life cases was questioned by some communication scholars, leading to a criticism of this methodology as not being able to capture what the respondent would do in a real-life situation. A research study addressed this criticism by comparatively testing a spiral model both in a hypothetical survey and in a focus group. The findings are in line with the critic of hypothetical survey questions, demonstrating a significant increase in the spiral of silence in focus groups.

Among different approaches to survey methodology, cross-sectional study design is the leading method employed to analyze and test the theory. Cross-sectional design involves the analysis of the relationship between public opinion and willingness to speak at one point in time.

While many of the researchers employ cross-sectional design, some scholars employed panel data. Under this methodology, three specific approaches have been used. Noelle-Neumann herself tested the theory from the aggregate level. Using this approach, the change process is "observed by comparing the absolute share of people perceiving a majority climate with people willing to express their views over time." The second approach that has been used in Spiral of Silence research is conducting separate regressions for each panel survey wave. The drawback for this approach is that the individual change of climate and opinions perception is ignored. The last approach a few scholars used in conducting Spiral of Silence researches is to use changed scores as dependent variables. However, as intuitive as this approach may be, it "leads to well-documented difficulties with respect to statistical properties, such as regression to the mean or the negative correlation of the change score with the time one state".

Criticisms

The critics of this theory most often claim that individuals have different influences that affect whether they speak out or not.

Research indicates that people fear isolation in their small social circles more than they do in the population at large. Within a large nation, one can always find a group of people who share one's opinions, however people fear isolation from their close family and friends more in theory. Research has demonstrated that this fear of isolation is stronger than the fear of being isolated from the entire public, as it is typically measured.

Scholars have also argued that both personal characteristics and various culture among different groups will have influences on whether a person will willingly speak out. If one person "has a positive self-concept and lacks a sense of shame, that person will speak out regardless of how she or he perceives the climate of public opinion." Another influence critics give for people choosing not to speak out against public opinion is culture. Open expression of ideas is forbidden in some of the cultures. Some cultures are more individualistic, which would support more of an individual's own opinion, while collectivist cultures support the overall group's opinion and needs. Gender can be also considered as a cultural factor. In some cultures, women's "perception of language, not public opinion, forces them to remain quiet." Scheufele & Moy, further assert that certain conflict styles and cultural indicators should be used to understand these differences.

The nature of issues will influence the dynamic processes of the spiral of silence. Yeric and Todd present three issues type, including enduring issues that will be discussed by the public for a long time; emerging issues that are new to the public but have the potential to become enduring issues; and the transitory issues, which don't stay in the public consciousness for very long but come up from time to time. The research suggests that issues difference affects people's willingness to express. Facebook users are more likely to post their real thoughts on emerging issues such as gay marriage in an incongruent opinion climate.

Another criticism of the spiral of silence research is that the research designs do not observe the movement in the spiral over time. Critics propose that Noelle-Neumann's emphasis on time in the formation of the spiral should reflect on the methodology as well, and the dynamic nature of the spiral model should be acknowledged. They argue that the spiral of silence theory involves a "time factor", considering that the changes in public opinion eventually lead to change in people's assessments of the public opinion. Also, according to Spilchal, the spiral of silence theory "ignores the evidence of the historical development of public opinion, both in theory and practice, through the extension of suffrage, organisation of political propaganda groups, the establishment of pressure groups and political parties, the eligibility of ever wider circles of public officials and, eventually, the installation of several forms of direct democracy."

Some scholars also provide understandings of the theory in the contemporary society by pointing out that "it is not so much the actual statistical majority that generates pressure for conformity as it is the climate of opinion conveyed in large measure by the media." Under the great influence by the media coverage, the climate of opinion "is not invariably an accurate reflection of the distribution of opinions within the polity."

Further, Scheufele & Moy find problems in the operationalization of key terms, including willingness to speak out. This construct should be measured in terms of actually speaking out, not voting or other conceptually similar constructs. Conformity experiments have no moral component, yet morality is a key construct in the model. These conformity experiments, particularly those by Asch, form part of the base of the theory. Scholars question whether these conformity experiments are relevant to the development of the Spiral of Silence.

False dilemmas and silence of consistency

Research indicates that while the existence of groups with other opinions than those that are supposed to be dominant in a society opens a possibility for some people to express some different opinions, fallacy assumptions in such groups that criticism of particular aspects of that group's program is support for society's mainstream views is a source of false dilemmas. This research indicates that such false dilemmas, especially when there are inconsistencies both in mainstream views and in organized opposition views, causes a spiral of silence that specifically silences logically consistent third, fourth or higher number viewpoint criticism. The research in question does not find a solution in many approaches of "recognizing cognitive bias" but instead indicate that such assumptions are part of the problem by promoting the myth of one's own group having overcome its bias by institutional means and allegations of rational critical arguments being due to bias in the minds of critics, citing evolutionary research that shows that not only would any predisposition for justification of views be selected against due to costing nutrients without improving adaptivity of behavior, but that the claim that most adult humans are irrational due to missing stimulation of rationality in early childhood is also evolutionarily indefensible as genes for potential rationality would have been totally eliminated by selection before reaching significant population fraction if they needed a society already promoting rationality to manifest themselves adaptively. The research indicates that humans are not inherently irrational but are forced to pretend irrationality by false dilemmas that claim rational criticism to be justifications for irrational resentment, and suggest that openly expressed rationality can be promoted by discussions in which no exclusion based on traditional political scales or beneficiary classifications exist but all allegations of irrational motives as well as assumptions that some opinions are linked or that criticism of one view is defence of another specific view are excluded.

Concentrated solar power

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Concentrated_solar_power 

A solar power tower at Crescent Dunes Solar Energy Project concentrating light via 10,000 mirrored heliostats spanning thirteen million sq ft (1.21 km²).

 

The three towers of the Ivanpah Solar Power Facility

 

Part of the 354 MW SEGS solar complex in northern San Bernardino County, California

 

Bird's eye view of Khi Solar One, South Africa

Concentrated solar power (CSP, also known as concentrating solar power, concentrated solar thermal) systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight onto a receiver. Electricity is generated when the concentrated light is converted to heat (solar thermal energy), which drives a heat engine (usually a steam turbine) connected to an electrical power generator or powers a thermochemical reaction.

CSP had a global total installed capacity of 5,500 MW in 2018, up from 354 MW in 2005. Spain accounted for almost half of the world's capacity, at 2,300 MW, despite no new capacity entering commercial operation in the country since 2013. The United States follows with 1,740 MW. Interest is also notable in North Africa and the Middle East, as well as India and China. The global market was initially dominated by parabolic-trough plants, which accounted for 90% of CSP plants at one point. Since about 2010, central power tower CSP has been favored in new plants due to its higher temperature operation – up to 565 °C (1,049 °F) vs. trough's maximum of 400 °C (752 °F) – which promises greater efficiency.

Among the larger CSP projects are the Ivanpah Solar Power Facility (392 MW) in the United States, which uses solar power tower technology without thermal energy storage, and the Ouarzazate Solar Power Station in Morocco, which combines trough and tower technologies for a total of 510 MW with several hours of energy storage.

As a thermal energy generating power station, CSP has more in common with thermal power stations such as coal, gas, or geothermal. A CSP plant can incorporate thermal energy storage, which stores energy either in the form of sensible heat or as latent heat (for example, using molten salt), which enables these plants to continue to generate electricity whenever it is needed, day or night. This makes CSP a dispatchable form of solar. Dispatchable renewable energy is particularly valuable in places where there is already a high penetration of photovoltaics (PV), such as California because demand for electric power peaks near sunset just as PV capacity ramps down (a phenomenon referred to as duck curve).

CSP is often compared to photovoltaic solar (PV) since they both use solar energy. While solar PV experienced huge growth in recent years due to falling prices, Solar CSP growth has been slow due to technical difficulties and high prices. In 2017, CSP represented less than 2% of worldwide installed capacity of solar electricity plants. However, CSP can more easily store energy during the night, making it more competitive with dispatchable generators and baseload plants.

The DEWA project in Dubai, under construction in 2019, held the world record for lowest CSP price in 2017 at US$73 per MWh for its 700 MW combined trough and tower project: 600 MW of trough, 100 MW of tower with 15 hours of thermal energy storage daily. Base-load CSP tariff in the extremely dry Atacama region of Chile reached below $50/MWh in 2017 auctions.

History

Solar steam engine for water pumping, near Los Angeles circa 1901

A legend has it that Archimedes used a "burning glass" to concentrate sunlight on the invading Roman fleet and repel them from Syracuse. In 1973 a Greek scientist, Dr. Ioannis Sakkas, curious about whether Archimedes could really have destroyed the Roman fleet in 212 BC, lined up nearly 60 Greek sailors, each holding an oblong mirror tipped to catch the sun's rays and direct them at a tar-covered plywood silhouette 49 m (160 ft) away. The ship caught fire after a few minutes; however, historians continue to doubt the Archimedes story.

In 1866, Auguste Mouchout used a parabolic trough to produce steam for the first solar steam engine. The first patent for a solar collector was obtained by the Italian Alessandro Battaglia in Genoa, Italy, in 1886. Over the following years, invеntors such as John Ericsson and Frank Shuman developed concentrating solar-powered dеvices for irrigation, refrigеration, and locomоtion. In 1913 Shuman finished a 55 horsepower (41 kW) parabolic solar thermal energy station in Maadi, Egypt for irrigation. The first solar-power system using a mirror dish was built by Dr. R.H. Goddard, who was already well known for his research on liquid-fueled rockets and wrote an article in 1929 in which he asserted that all the previous obstacles had been addressed.

Professor Giovanni Francia (1911–1980) designed and built the first concentrated-solar plant, which entered into operation in Sant'Ilario, near Genoa, Italy in 1968. This plant had the architecture of today's power tower plants with a solar receiver in the center of a field of solar collectors. The plant was able to produce 1 MW with superheated steam at 100 bar and 500 °C. The 10 MW Solar One power tower was developed in Southern California in 1981. Solar One was converted into Solar Two in 1995, implementing a new design with a molten salt mixture (60% sodium nitrate, 40% potassium nitrate) as the receiver working fluid and as a storage medium. The molten salt approach proved effective, and Solar Two operated successfully until it was decommissioned in 1999. The parabolic-trough technology of the nearby Solar Energy Generating Systems (SEGS), begun in 1984, was more workable. The 354 MW SEGS was the largest solar power plant in the world, until 2014.

No commercial concentrated solar was constructed from 1990 when SEGS was completed until 2006 when the Compact linear Fresnel reflector system at Liddell Power Station in Australia was built. Few other plants were built with this design although the 5 MW Kimberlina Solar Thermal Energy Plant opened in 2009.

In 2007, 75 MW Nevada Solar One was built, a trough design and the first large plant since SEGS. Between 2009 and 2013, Spain built over 40 parabolic trough systems, standardized in 50 MW blocks.

Due to the success of Solar Two, a commercial power plant, called Solar Tres Power Tower, was built in Spain in 2011, later renamed Gemasolar Thermosolar Plant. Gemasolar's results paved the way for further plants of its type. Ivanpah Solar Power Facility was constructed at the same time but without thermal storage, using natural gas to preheat water each morning.

Most concentrated solar power plants use the parabolic trough design, instead of the power tower or Fresnel systems. There have also been variations of parabolic trough systems like the integrated solar combined cycle (ISCC) which combines troughs and conventional fossil fuel heat systems.

CSP was originally treated as a competitor to photovoltaics, and Ivanpah was built without energy storage, although Solar Two had included several hours of thermal storage. By 2015, prices for photovoltaic plants had fallen and PV commercial power was selling for 1⁄3 of recent CSP contracts. However, increasingly, CSP was being bid with 3 to 12 hours of thermal energy storage, making CSP a dispatchable form of solar energy. As such, it is increasingly seen as competing with natural gas and PV with batteries for flexible, dispatchable power.

Current technology

CSP is used to produce electricity (sometimes called solar thermoelectricity, usually generated through steam). Concentrated-solar technology systems use mirrors or lenses with tracking systems to focus a large area of sunlight onto a small area. The concentrated light is then used as heat or as a heat source for a conventional power plant (solar thermoelectricity). The solar concentrators used in CSP systems can often also be used to provide industrial process heating or cooling, such as in solar air conditioning.

Concentrating technologies exist in four optical types, namely parabolic trough, dish, concentrating linear Fresnel reflector, and solar power tower. Parabolic trough and concentrating linear Fresnel reflectors are classified as linear focus collector types, while dish and solar tower are point focus types. Linear focus collectors achieve medium concentration factors (50 suns and over), and point focus collectors achieve high concentration factors (over 500 suns). Although simple, these solar concentrators are quite far from the theoretical maximum concentration. For example, the parabolic-trough concentration gives about 1⁄3 of the theoretical maximum for the design acceptance angle, that is, for the same overall tolerances for the system. Approaching the theoretical maximum may be achieved by using more elaborate concentrators based on nonimaging optics.

Different types of concentrators produce different peak temperatures and correspondingly varying thermodynamic efficiencies, due to differences in the way that they track the sun and focus light. New innovations in CSP technology are leading systems to become more and more cost-effective.

Parabolic trough

Main article: Parabolic trough

 

Parabolic trough at a plant near Harper Lake, California

A parabolic trough consists of a linear parabolic reflector that concentrates light onto a receiver positioned along the reflector's focal line. The receiver is a tube positioned at the longitudinal focal line of the parabolic mirror and filled with a working fluid. The reflector follows the sun during the daylight hours by tracking along a single axis. A working fluid (e.g. molten salt) is heated to 150–350 °C (302–662 °F) as it flows through the receiver and is then used as a heat source for a power generation system. Trough systems are the most developed CSP technology. The Solar Energy Generating Systems (SEGS) plants in California, the world's first commercial parabolic trough plants, Acciona's Nevada Solar One near Boulder City, Nevada, and Andasol, Europe's first commercial parabolic trough plant are representative, along with Plataforma Solar de Almería's SSPS-DCS test facilities in Spain.

Enclosed trough

The design encapsulates the solar thermal system within a greenhouse-like glasshouse. The glasshouse creates a protected environment to withstand the elements that can negatively impact reliability and efficiency of the solar thermal system. Lightweight curved solar-reflecting mirrors are suspended from the ceiling of the glasshouse by wires. A single-axis tracking system positions the mirrors to retrieve the optimal amount of sunlight. The mirrors concentrate the sunlight and focus it on a network of stationary steel pipes, also suspended from the glasshouse structure. Water is carried throughout the length of the pipe, which is boiled to generate steam when intense solar radiation is applied. Sheltering the mirrors from the wind allows them to achieve higher temperature rates and prevents dust from building up on the mirrors.

GlassPoint Solar, the company that created the Enclosed Trough design, states its technology can produce heat for Enhanced Oil Recovery (EOR) for about $5 per 290 kWh (1,000,000 BTU) in sunny regions, compared to between $10 and $12 for other conventional solar thermal technologies.

Solar power tower

Main article: Solar power tower

 

Ashalim Power Station, Israel, on its completion the tallest solar tower in the world. It concentrates light from over 50,000 heliostats.

 

The PS10 solar power plant in Andalusia, Spain concentrates sunlight from a field of heliostats onto a central solar power tower.

A solar power tower consists of an array of dual-axis tracking reflectors (heliostats) that concentrate sunlight on a central receiver atop a tower; the receiver contains a heat-transfer fluid, which can consist of water-steam or molten salt. Optically a solar power tower is the same as a circular Fresnel reflector. The working fluid in the receiver is heated to 500–1000 °C (773–1,273 K or 932–1,832 °F) and then used as a heat source for a power generation or energy storage system. An advantage of the solar tower is the reflectors can be adjusted instead of the whole tower. Power-tower development is less advanced than trough systems, but they offer higher efficiency and better energy storage capability. Beam down tower application is also feasible with heliostats to heat the working fluid.

The Solar Two in Daggett, California and the CESA-1 in Plataforma Solar de Almeria Almeria, Spain, are the most representative demonstration plants. The Planta Solar 10 (PS10) in Sanlucar la Mayor, Spain, is the first commercial utility-scale solar power tower in the world. The 377 MW Ivanpah Solar Power Facility, located in the Mojave Desert, is the largest CSP facility in the world, and uses three power towers. Ivanpah generated only 0.652 TWh (63%) of its energy from solar means, and the other 0.388 TWh (37%) was generated by burning natural gas. 

Fresnel reflectors

Main article: Compact linear Fresnel reflector

Fresnel reflectors are made of many thin, flat mirror strips to concentrate sunlight onto tubes through which working fluid is pumped. Flat mirrors allow more reflective surface in the same amount of space than a parabolic reflector, thus capturing more of the available sunlight, and they are much cheaper than parabolic reflectors. Fresnel reflectors can be used in various size CSPs.

Fresnel reflectors are sometimes regarded as a technology with a worse output than other methods. The cost efficiency of this model is what causes some to use this instead of others with higher output ratings. Some new models of Fresnel Reflectors with Ray Tracing capabilities have begun to be tested and have initially proved to yield higher output than the standard version.

Dish Stirling

See also: Solar thermal energy § Dish designs

 

A dish Stirling

A dish Stirling or dish engine system consists of a stand-alone parabolic reflector that concentrates light onto a receiver positioned at the reflector's focal point. The reflector tracks the Sun along two axes. The working fluid in the receiver is heated to 250–700 °C (482–1,292 °F) and then used by a Stirling engine to generate power. Parabolic-dish systems provide high solar-to-electric efficiency (between 31% and 32%), and their modular nature provides scalability. The Stirling Energy Systems (SES), United Sun Systems (USS) and Science Applications International Corporation (SAIC) dishes at UNLV, and Australian National University's Big Dish in Canberra, Australia are representative of this technology. A world record for solar to electric efficiency was set at 31.25% by SES dishes at the National Solar Thermal Test Facility (NSTTF) in New Mexico on 31 January 2008, a cold, bright day. According to its developer, Ripasso Energy, a Swedish firm, in 2015 its Dish Sterling system being tested in the Kalahari Desert in South Africa showed 34% efficiency. The SES installation in Maricopa, Phoenix was the largest Stirling Dish power installation in the world until it was sold to United Sun Systems. Subsequently, larger parts of the installation have been moved to China as part of the huge energy demand.

Solar thermal enhanced oil recovery

Main article: Solar thermal enhanced oil recovery

Heat from the sun can be used to provide steam used to make heavy oil less viscous and easier to pump. Solar power tower and parabolic troughs can be used to provide the steam which is used directly so no generators are required and no electricity is produced. Solar thermal enhanced oil recovery can extend the life of oilfields with very thick oil which would not otherwise be economical to pump.

CSP with thermal energy storage

See also: Thermal energy storage and Solar thermal energy

In a CSP plant that includes storage, the solar energy is first used to heat the molten salt or synthetic oil which is stored providing thermal/heat energy at high temperature in insulated tanks. Later the hot molten salt (or oil) is used in a steam generator to produce steam to generate electricity by steam turbo generator as per requirement. Thus solar energy which is available in daylight only is used to generate electricity round the clock on demand as a load following power plant or solar peaker plant. The thermal storage capacity is indicated in hours of power generation at nameplate capacity. Unlike solar PV or CSP without storage, the power generation from solar thermal storage plants is dispatchable and self-sustainable similar to coal/gas-fired power plants, but without the pollution. CSP with thermal energy storage plants can also be used as cogeneration plants to supply both electricity and process steam round the clock. As of December 2018, CSP with thermal energy storage plants generation cost have ranged between 5 c € / kWh and 7 c € / kWh depending on good to medium solar radiation received at a location. Unlike solar PV plants, CSP with thermal energy storage plants can also be used economically round the clock to produce only process steam replacing pollution emitting fossil fuels. CSP plant can also be integrated with solar PV for better synergy.

CSP with thermal storage systems are also available using Brayton cycle with air instead of steam for generating electricity and/or steam round the clock. These CSP plants are equipped with gas turbine to generate electricity. These are also small in capacity (<0.4 MW) with flexibility to install in few acres area. Waste heat from the power plant can also be used for process steam generation and HVAC needs. In case land availability is not a limitation, any number of these modules can be installed up to 1000 MW with RAMS and cost advantage since the per MW cost of these units are cheaper than bigger size solar thermal stations.

Centralized district heating round the clock is also feasible with concentrated solar thermal storage plants.

Carbon neutral fuels production

Carbon neutral synthetic fuels production using concentrated solar thermal energy at nearly 1500 °C temperature is feasible technically and viable commercially in near future with declining costs of CSP plants. Also carbon neutral hydrogen can be produced with solar thermal energy (CSP) using Sulfur–iodine cycle, Hybrid sulfur cycle, Iron oxide cycle, Copper–chlorine cycle, Zinc–zinc oxide cycle, Cerium(IV) oxide–cerium(III) oxide cycle, etc.

Deployment around the world

Main articles: List of solar thermal power stations and Solar power by country

 

National CSP capacities in 2018 (MW_p)

Country	Total	Added
Spain	2,300	0
United States	1,738	0
South Africa	400	100
Morocco	380	200
India	225	0
China	210	200
United Arab Emirates	100	0
Saudi Arabia	50	50
Algeria	25	0
Egypt	20	0
Australia	12	0
Thailand	5	0
Source: REN21 Global Status Report, 2017 and 2018

The commercial deployment of CSP plants started by 1984 in the US with the SEGS plants. The last SEGS plant was completed in 1990. From 1991 to 2005, no CSP plants were built anywhere in the world. Global installed CSP-capacity increased nearly tenfold between 2004 and 2013 and grew at an average of 50 percent per year during the last five of those years. In 2013, worldwide installed capacity increased by 36% or nearly 0.9 gigawatt (GW) to more than 3.4 GW. Spain and the United States remained the global leaders, while the number of countries with installed CSP were growing but the rapid decrease in price of PV solar, policy changes and the global financial crisis stopped most development in these countries. 2014 was the best year for CSP but was followed by a rapid decline with only one major plant completed in the world in 2016. There is a notable trend towards developing countries and regions with high solar radiation with several large plants under construction in 2017.

Efficiency

The efficiency of a concentrating solar power system will depend on the technology used to convert the solar power to electrical energy, the operating temperature of the receiver and the heat rejection, thermal losses in the system, and the presence or absence of other system losses; in addition to the conversion efficiency, the optical system which concentrates the sunlight will also add additional losses.

Real-world systems claim a maximum conversion efficiency of 23-35% for "power tower" type systems, operating at temperatures from 250 to 565 °C, with the higher efficiency number assuming a combined cycle turbine. Dish Stirling systems, operating at temperatures of 550-750 °C, claim an efficiency of about 30%. Due to variation in sun incidence during the day, the average conversion efficiency achieved is not equal to these maximum efficiencies, and the net annual solar-to- electricity efficiencies are 7-20% for pilot power tower systems, and 12-25% for demonstration-scale Stirling dish systems.

Theory

The maximum conversion efficiency of any thermal to electrical energy system is given by the Carnot efficiency, which represents a theoretical limit to the efficiency that can be achieved by any system, set by the laws of thermodynamics. Real-world systems do not achieve the Carnot efficiency.

The conversion efficiency ${\displaystyle \eta }$ of the incident solar radiation into mechanical work depends on the thermal radiation properties of the solar receiver and on the heat engine (e.g. steam turbine). Solar irradiation is first converted into heat by the solar receiver with the efficiency ${\displaystyle \eta _{Receiver}}$ and subsequently the heat is converted into mechanical energy by the heat engine with the efficiency ${\displaystyle \eta _{mechanical}}$, using Carnot's principle. The mechanical energy is then converted into electrical energy by a generator. For a solar receiver with a mechanical converter (e.g., a turbine), the overall conversion efficiency can be defined as follows:

${\displaystyle \eta =\eta _{\mathrm {optics} }\cdot \eta _{\mathrm {receiver} }\cdot \eta _{\mathrm {mechanical} }\cdot \eta _{\mathrm {generator} }}$

where ${\displaystyle \eta _{\mathrm {optics} }}$ represents the fraction of incident light concentrated onto the receiver, ${\displaystyle \eta _{\mathrm {receiver} }}$ the fraction of light incident on the receiver that is converted into heat energy, ${\displaystyle \eta _{\mathrm {mechanical} }}$ the efficiency of conversion of heat energy into mechanical energy, and ${\displaystyle \eta _{\mathrm {generator} }}$ the efficiency of converting the mechanical energy into electrical power.

${\displaystyle \eta _{\mathrm {receiver} }}$ is:

${\displaystyle \eta _{\mathrm {receiver} }={\frac {Q_{\mathrm {absorbed} }-Q_{\mathrm {lost} }}{Q_{\mathrm {incident} }}}}$

with ${\displaystyle Q_{\mathrm {incident} }}$, ${\displaystyle Q_{\mathrm {absorbed} }}$, ${\displaystyle Q_{\mathrm {lost} }}$ respectively the incoming solar flux and the fluxes absorbed and lost by the system solar receiver.

The conversion efficiency ${\displaystyle \eta _{\mathrm {mechanical} }}$ is at most the Carnot efficiency, which is determined by the temperature of the receiver ${\displaystyle T_{H}}$ and the temperature of the heat rejection ("heat sink temperature") ${\displaystyle T^{0}}$,

${\displaystyle \eta _{\mathrm {Carnot} }=1-{\frac {T^{0}}{T_{H}}}}$

The real-world efficiencies of typical engines achieve 50% to at most 70% of the Carnot efficiency due to losses such as heat loss and windage in the moving parts.

Ideal case

For a solar flux ${\displaystyle I}$ (e.g. ${\displaystyle I=1000\,\mathrm {W/m^{2}} }$) concentrated ${\displaystyle C}$ times with an efficiency ${\displaystyle \eta _{Optics}}$ on the system solar receiver with a collecting area ${\displaystyle A}$ and an absorptivity ${\displaystyle \alpha }$:

${\displaystyle Q_{\mathrm {solar} }=ICA}$,

${\displaystyle Q_{\mathrm {absorbed} }=\eta _{\mathrm {optics} }\alpha Q_{\mathrm {solar} }}$,

For simplicity's sake, one can assume that the losses are only radiative ones (a fair assumption for high temperatures), thus for a reradiating area A and an emissivity ${\displaystyle \epsilon }$ applying the Stefan–Boltzmann law yields:

${\displaystyle Q_{\mathrm {lost} }=A\epsilon \sigma T_{H}^{4}}$

Simplifying these equations by considering perfect optics (${\displaystyle \eta _{\mathrm {Optics} }}$ = 1) and without considering the ultimate conversion step into electricity by a generator, collecting and reradiating areas equal and maximum absorptivity and emissivity (${\displaystyle \alpha }$ = 1, ${\displaystyle \epsilon }$ = 1) then substituting in the first equation gives

${\displaystyle \eta =\left(1-{\frac {\sigma T_{H}^{4}}{IC}}\right)\cdot \left(1-{\frac {T^{0}}{T_{H}}}\right)}$

The graph shows that the overall efficiency does not increase steadily with the receiver's temperature. Although the heat engine's efficiency (Carnot) increases with higher temperature, the receiver's efficiency does not. On the contrary, the receiver's efficiency is decreasing, as the amount of energy it cannot absorb (Q_lost) grows by the fourth power as a function of temperature. Hence, there is a maximum reachable temperature. When the receiver efficiency is null (blue curve on the figure below), T_max is: ${\displaystyle T_{\mathrm {max} }=\left({\frac {IC}{\sigma }}\right)^{0.25}}$

There is a temperature T_opt for which the efficiency is maximum, i.e. when the efficiency derivative relative to the receiver temperature is null:

${\displaystyle {\frac {d\eta }{dT_{H}}}(T_{\mathrm {opt} })=0}$

Consequently, this leads us to the following equation:

${\displaystyle T_{opt}^{5}-(0.75T^{0})T_{\mathrm {opt} }^{4}-{\frac {T^{0}IC}{4\sigma }}=0}$

Solving this equation numerically allows us to obtain the optimum process temperature according to the solar concentration ratio ${\displaystyle C}$ (red curve on the figure below)

C	500	1000	5000	10000	45000 (max. for Earth)
Tmax	1720	2050	3060	3640	5300
Topt	970	1100	1500	1720	2310

Theoretical efficiencies aside, real-world experience of CSP reveals a 25%–60% shortfall in projected production, a good part of which is due to the practical Carnot cycle losses not included in the above analysis.

Cost

As early as 2011, the rapid decline of the price of photovoltaic systems lead to projections that CSP will no longer be economically viable. As of 2020, the least expensive utility-scale concentrated solar power stations in the United States and worldwide are five times more expensive than utility-scale photovoltaic power stations, with a projected minimum price of 7 cents per kilowatt-hour for the most advanced CSP stations against record lows of 1.32 cents per kWh for utility-scale PV. This five-fold price difference has been maintained since 2018.

Even though overall deployment of CSP remains limited the levelized cost of power from commercial scale plants has decreased significantly in recent years. With a learning rate estimated at around 20% cost reduction of every doubling in capacity the cost were approaching the upper end of the fossil fuel cost range at the beginning of the 2020s driven by support schemes in several countries, including Spain, the US, Morocco, South Africa, China, and the UAE: 

 

CSP deployment has slowed down considerably as most of the above-mentioned markets have cancelled their support, as the technology turned out to be more expensive on a per kWH basis than solar PV and wind power. CSP in combination with Thermal Energy Storage (TES) is expected by some to become cheaper than PV with lithium batteries for storage durations above 4 hours per day, while NREL expects that by 2030 PV with 10-hour storage lithium batteries will cost the same as PV with 4-hour storage used to cost in 2020.

Incentives and Markets

Spain

Andasol Solar Power Station in Spain

In 2008 Spain launched the first commercial scale CSP market in Europe. Until 2012, solar-thermal electricity generation was initially eligible for feed-in tariff payments (art. 2 RD 661/2007) - leading to the creation of the largest CSP fleet in the world which at 2.3 GW of installed capacity contributes about 5TWh of power to the Spanish grid every year. The initial requirements for plants in the FiT were:

• Systems registered in the register of systems prior to 29 September 2008: 50 MW for solar-thermal systems.
• Systems registered after 29 September 2008 (PV only).

The capacity limits for the different system types were re-defined during the review of the application conditions every quarter (art. 5 RD 1578/2008, Annex III RD 1578/2008). Prior to the end of an application period, the market caps specified for each system type are published on the website of the Ministry of Industry, Tourism and Trade (art. 5 RD 1578/2008). Because of cost concerns Spain has halted acceptance of new projects for the feed-in-tariff on 27 January 2012  Already accepted projects were affected by a 6% "solar-tax" on feed-in-tariffs, effectively reducing the feed-in-tariff.

In this context, the Spanish Government enacted the Royal Decree-Law 9/2013 in 2013, aimed at the adoption of urgent measures to guarantee the economic and financial stability of the electric system, laying the foundations of the new Law 24/2013 of the Spanish electricity sector. This new retroactive legal-economic framework applied to all the renewable energy systems was developed in 2014 by the RD 413/2014, which abolished the former regulatory frameworks set by the RD 661/2007 and the RD 1578/2008 and defined a new remuneration scheme for these assets.

After a lost decade for CSP in Europe, Spain announced it its National Energy and Climate Plan the intention of adding 5GW of CSP capacity between 2021 and 2030. Towards this end bi-annual auctions of 200 MW of CSP capacity starting in 2021 are expected, but details are not yet known.

Australia

Main article: Solar power in Australia

Several CSP dishes have been set up in remote Aboriginal settlements in the Northern Territory: Hermannsburg, Yuendumu and Lajamanu.

So far no commercial scale CSP project has been commissioned in Australia, but several projects were suggested. In 2017 now bankrupt American CSP developer SolarReserve got awarded a PPA to realize the 150MW Aurora Solar Thermal Power Project in South Australia at a record low rate of just AUD$0.08/kWh or close to USD$0.06/kWh. Unfortunately the company failed to secure financing and the project got cancelled. Another promising application for CSP in Australia are mines that need 24/7 electricity but often have no grid connection. Vast Solar a startup company aiming to commercialize a novel modular third generation CSP design is looking to start construction of a 50MW combines CSP and PV facility in Mt. Isa of North-West Queensland in 2021.

At the federal level, under the Large-scale Renewable Energy Target (LRET), in operation under the Renewable Energy Electricity Act 2000, large scale solar thermal electricity generation from accredited RET power stations may be entitled to create large-scale generation certificates (LGCs). These certificates can then be sold and transferred to liable entities (usually electricity retailers) to meet their obligations under this tradeable certificates scheme. However, as this legislation is technology neutral in its operation, it tends to favour more established RE technologies with a lower levelised cost of generation, such as large scale onshore wind, rather than solar thermal and CSP. At State level, renewable energy feed-in laws typically are capped by maximum generation capacity in kWp, and are open only to micro or medium scale generation and in a number of instances are only open to solar PV (photovoltaic) generation. This means that larger scale CSP projects would not be eligible for payment for feed-in incentives in many of the State and Territory jurisdictions.

China

In 2016 China announced its intention to build a batch of 20 technologically diverse CSP demonstration projects in the context of the 13th Five-Year Plan, with the intention of building up an internationally competitive CSP industry. Since the first plants were completed in 2018, the generated electricity from the plants with thermal storage is supported with an administratively set FiT of RMB 1.5 per kWh. At the end of 2020, China operated a total of 545 MW in 12 CSP plants, seven plants (320 MW) are molten-salt towers; another two plants (150MW) use the proven Eurotrough 150 parabolic trough design, three plants (75 MW) use liner fresnel collectors. Plans to build a second batch of demonstration projects were never enacted and further technology specific support for CSP in the upcoming 14th Five-Year Plan is unknown. Current support is set for remaining projects from the demonstration batch and will run out at the end of 2021.

India

In March 2020, SECI called for 5000 MW tenders which can be combination of Solar PV, Solar thermal with storage and Coal based power (minimum 51% from renewable sources) to supply round the clock power at minimum 80% yearly availability.

Future

A study done by Greenpeace International, the European Solar Thermal Electricity Association, and the International Energy Agency's SolarPACES group investigated the potential and future of concentrated solar power. The study found that concentrated solar power could account for up to 25% of the world's energy needs by 2050. The increase in investment would be from €2 billion worldwide to €92.5 billion in that time period. Spain is the leader in concentrated solar power technology, with more than 50 government-approved projects in the works. Also, it exports its technology, further increasing the technology's stake in energy worldwide. Because the technology works best with areas of high insolation (solar radiation), experts predict the biggest growth in places like Africa, Mexico, and the southwest United States. It indicates that the thermal storage systems based in nitrates (calcium, potassium, sodium,...) will make the CSP plants more and more profitable. The study examined three different outcomes for this technology: no increases in CSP technology, investment continuing as it has been in Spain and the US, and finally the true potential of CSP without any barriers on its growth. The findings of the third part are shown in the table below:

Year	Annual Investment	Cumulative Capacity
2015	€21 billion	4,755 MW
2050	€174 billion	1,500,000 MW

Finally, the study acknowledged how technology for CSP was improving and how this would result in a drastic price decrease by 2050. It predicted a drop from the current range of €0.23–0.15/kWh to €0.14–0.10/kWh.

The European Union looked into developing a €400 billion (US$774 billion) network of solar power plants based in the Sahara region using CSP technology to be known as Desertec, to create "a new carbon-free network linking Europe, the Middle East and North Africa". The plan was backed mainly by German industrialists and predicted production of 15% of Europe's power by 2050. Morocco was a major partner in Desertec and as it has barely 1% of the electricity consumption of the EU, it could produce more than enough energy for the entire country with a large energy surplus to deliver to Europe. Algeria has the biggest area of desert, and private Algerian firm Cevital signed up for Desertec. With its wide desert (the highest CSP potential in the Mediterranean and Middle East regions ~ about 170 TWh/year) and its strategic geographical location near Europe, Algeria is one of the key countries to ensure the success of Desertec project. Moreover, with the abundant natural-gas reserve in the Algerian desert, this will strengthen the technical potential of Algeria in acquiring Solar-Gas Hybrid Power Plants for 24-hour electricity generation. Most of the participants pulled out of the effort at the end of 2014.

Experience with first-of-a-kind CSP plants in the USA was mixed. Solana in Arizona, and Ivanpah in California indicate large production shortfalls in electricity generation between 25% and 40% in the first years of operation. Producers blame clouds and stormy weather, but critics seem to think there are technological issues. These problems are causing utilities to pay inflated prices for wholesale electricity, and threaten the long-term viability of the technology. As photovoltaic costs continue to plummet, many think CSP has a limited future in utility-scale electricity production. In other countries especially Spain and South Africa CSP plants have met their designed parameters 

CSP has other uses than electricity. Researchers are investigating solar thermal reactors for the production of solar fuels, making solar a fully transportable form of energy in the future. These researchers use the solar heat of CSP as a catalyst for thermochemistry to break apart molecules of H₂O, to create hydrogen (H₂) from solar energy with no carbon emissions. By splitting both H₂O and CO₂, other much-used hydrocarbons – for example, the jet fuel used to fly commercial airplanes – could also be created with solar energy rather than from fossil fuels.

Very large scale solar power plants

There have been several proposals for gigawatt size, very-large-scale solar power plants. They include the Euro-Mediterranean Desertec proposal and Project Helios in Greece (10 GW), both now canceled. A 2003 study concluded that the world could generate 2,357,840 TWh each year from very large scale solar power plants using 1% of each of the world's deserts. Total consumption worldwide was 15,223 TWh/year (in 2003). The gigawatt size projects would have been arrays of standard-sized single plants. In 2012, the BLM made available 97,921,069 acres (39,627,251 hectares) of land in the southwestern United States for solar projects, enough for between 10,000 and 20,000 GW. The largest single plant in operation is the 510 MW Noor Solar Power Station. In 2022 the 700 MW CSP 4th phase of the 5GW Mohammed bin Rashid Al Maktoum Solar Park in Dubai will become the largest solar complex featuring CSP.

Suitable sites

The locations with highest direct irradiance are dry, at high altitude, and located in the tropics. These locations have a higher potential for CSP than areas with less sun.

Abandoned opencast mines, moderate hill slopes and crater depressions may be advantageous in the case of power tower CSP as the power tower can be located on the ground integral with the molten salt storage tank.

Environmental effects

CSP has a number of environmental effects, particularly on water use, land use and the use of hazardous materials. Water is generally used for cooling and to clean mirrors. Some projects are looking into various approaches to reduce the water and cleaning agents used, including the use of barriers, non-stick coatings on mirrors, water misting systems, and others.

Water use

Concentrating solar power plants with wet-cooling systems have the highest water-consumption intensities of any conventional type of electric power plant; only fossil-fuel plants with carbon-capture and storage may have higher water intensities. A 2013 study comparing various sources of electricity found that the median water consumption during operations of concentrating solar power plants with wet cooling was 3.1 cubic metres per megawatt-hour (810 US gal/MWh) for power tower plants and 3.4 m³/MWh (890 US gal/MWh) for trough plants. This was higher than the operational water consumption (with cooling towers) for nuclear at 2.7 m³/MWh (720 US gal/MWh), coal at 2.0 m³/MWh (530 US gal/MWh), or natural gas at 0.79 m³/MWh (210 US gal/MWh). A 2011 study by the National Renewable Energy Laboratory came to similar conclusions: for power plants with cooling towers, water consumption during operations was 3.27 m³/MWh (865 US gal/MWh) for CSP trough, 2.98 m³/MWh (786 US gal/MWh) for CSP tower, 2.60 m³/MWh (687 US gal/MWh) for coal, 2.54 m³/MWh (672 US gal/MWh) for nuclear, and 0.75 m³/MWh (198 US gal/MWh) for natural gas. The Solar Energy Industries Association noted that the Nevada Solar One trough CSP plant consumes 3.2 m³/MWh (850 US gal/MWh). The issue of water consumption is heightened because CSP plants are often located in arid environments where water is scarce.

In 2007, the US Congress directed the Department of Energy to report on ways to reduce water consumption by CSP. The subsequent report noted that dry cooling technology was available that, although more expensive to build and operate, could reduce water consumption by CSP by 91 to 95 percent. A hybrid wet/dry cooling system could reduce water consumption by 32 to 58 percent. A 2015 report by NREL noted that of the 24 operating CSP power plants in the US, 4 used dry cooling systems. The four dry-cooled systems were the three power plants at the Ivanpah Solar Power Facility near Barstow, California, and the Genesis Solar Energy Project in Riverside County, California. Of 15 CSP projects under construction or development in the US as of March 2015, 6 were wet systems, 7 were dry systems, 1 hybrid, and 1 unspecified.

Although many older thermoelectric power plants with once-through cooling or cooling ponds use more water than CSP, meaning that more water passes through their systems, most of the cooling water returns to the water body available for other uses, and they consume less water by evaporation. For instance, the median coal power plant in the US with once-through cooling uses 138 m³/MWh (36,350 US gal/MWh), but only 0.95 m³/MWh (250 US gal/MWh) (less than one percent) is lost through evaporation. Since the 1970s, the majority of US power plants have used recirculating systems such as cooling towers rather than once-through systems.

Effects on wildlife

Dead warbler burned in mid-air by solar thermal power plant

Insects can be attracted to the bright light caused by concentrated solar technology, and as a result birds that hunt them can be killed by being burned if they fly near the point where light is being focused. This can also affect raptors who hunt the birds. Federal wildlife officials were quoted by opponents as calling the Ivanpah power towers "mega traps" for wildlife.

Some media sources have reported that concentrated solar power plants have injured or killed large numbers of birds due to intense heat from the concentrated sunrays. Some of the claims may have been overstated or exaggerated.

According to rigorous reporting, in over six months, 133 singed birds were counted. By focusing no more than four mirrors on any one place in the air during standby, at Crescent Dunes Solar Energy Project, in three months, the death rate dropped to zero.